1. Field of the Invention
This invention relates generally to apparatus and method for energy delivery to dermatological tissue. More particularly, it relates to a systems and methods for delivering light via a handpiece that rolls or glides over skin or is generally moved from one location to another on the skin.
2. Description of the Related Art
Medical and aesthetic dermatological treatments are commonly performed by exposing skin to an appropriate quantity of energy at a wavelength absorbed by some component of the skin tissue. For example, energy can be targeted for selected absorption in blood vessels or hair follicles. Wrinkles, hyperpigmentation and scarring can be reduced by devices that target features of the water absorption spectrum. In some cases, a delivery mechanism that exposes only a fraction of the skin surface to light while sparing surrounding tissue may be preferred to a more aggressive treatment that ablates the full epidermis, because a fractional treatment reduces the risk of infection and better stimulates the wound healing response.
Prior medical laser systems have included mechanisms for controlling energy intensity, pulse duration, and size of treatment zones. Known methods often rely on both automated systems and interactive operator control to deliver an optimal treatment. One approach is to deliver light via a handpiece that gives the operator some degree of spatiotemporal control of exposure. Some handpieces are configured for delivering a fractional light exposure. A number of options exist for creating a pattern of exposure on the skin. Some systems deliver energy in a 2-D pattern that is stamped repeatedly onto the skin to cover the treatment area. Some known handpiece designs contain a single focused laser beam or an array of laser spots that are temporally controlled to produce a desired pattern as the handpiece moves over the skin. A subset of these systems also include a method for imaging the skin passing under the tip to calculate a tip velocity for feedback into a system that adjusts the pulse rate of the laser to accommodate changes in an operator's hand speed.
A common disadvantage of existing handpieces is that their automated control of laser focus, pulse rate and energy relies on the assumption that the operator will hold the handpiece normal to the skin surface. While a trained and conscientious clinician may be capable of approaching this level of precision, it is unreasonable to assume absolute consistency, especially in treatment of contoured regions of a treatment area, such as a face.
The consequences of handpiece misalignment depend on the details of the laser treatment. In a system with a 2-D fractional pattern, tilting the handpiece could distort the treatment pattern and shift the focal point of laser spots. The macroscopic result could be inhomogeneity of treatment with possible skin damage in regions of overexposure. A scanning handpiece with velocity feedback depends on normal orientation of the handpiece to properly track movement. Tilting the handpiece by a large angle could interrupt the delivery of treatment by triggering a safety shut-off in the tracking mechanism. This would result in undertreatment of that region of tissue. Even with a small error in angle, the focus of the laser could shift on both horizontal and vertical axes from its calculated target under the epidermis to some unspecified point outside of the treatment region.